1. Field of the Invention
The present invention relates generally to improvements in long underwater power distribution systems for sonar and other sensor systems, and more particularly pertains to a new and improved method and apparatus for branching a single wire underwater power distribution system.
2. Description of the Prior Art
A typical prior art single wire power distribution system 11 is shown in FIG. 1 wherein power is supplied to a plurality of nodes 13, 15 and 17 located under the ocean 25 (saltwater). The nodes are typically sonar or other transducer or sensor systems which require a source of power emanating from a shore or ship based power source 12. These prior art power delivery systems which utilize underwater cable have been optimized for use with a single wire 21 using the seawater 25 itself as a return 23. This approach minimizes cable weight because only one power wire instead of two is needed. Moreover, the seawater provides a lower resistance return path than an actual wire would for long runs.
In the prior art system illustrated in FIG. 1, power flow is from a shore based power source 12 through the conductive wire 21 in the cable, through each instrument and associated electronics node 13, 15 and 17 until the end of the cable is reached. At the end of the cable, a low impedance connection 19 is made to the seawater 25. This particular method efficiently delivers power over any length of cable to any desired number of instruments or electronic clusters (nodes). Typically, the power source on shore or ship is a constant current source with voltages supplied as required by each series node.
The disadvantage of this prior art series power delivery system is that it prevents the power conductor 21 from branching at any location along its length. The power source 12 located on shore or on a ship is a constant current source. If a branch or wire connection were to occur in the conductor 21, the current flow in each branch would be indeterminate. Both branches would be connected by low impedance 19 and 33, respectively, to the seawater for return. As shown in FIG. 2, branching the current path at point 27, for example, causing a single conductor 31 branch having a single node 29 therein with a lower voltage drop to receive all the current, while the other branch 21 with two nodes 13 and 15 therein, with a higher voltage drop, would receive no current. Such a parallel path system would not work.
And yet in many cases, a series only connection of electronic nodes is not optimum. For example, if an area of the ocean is to be populated with an evenly spaced grid of instruments such as shown in FIG. 3, a series only connection scheme would require the cable to zigzag back and forth many times between the various nodes 13, 15, 17, 35 and 37, increasing power loss and installation cost.
A shorter total cable length would be obtained if series and parallel node connections are allowed as shown in FIG. 4. As can be seen from FIG. 4, the parallel branching connections provide for a minimum of cable length for any installation. However, a direct implementation of a parallel path system will not work, as discussed above.
Furthermore, cable installation is frequently required to be modified at some later date. If all the nodes are in series, such modification becomes very difficult. New nodes may only be added at the end of a cable. Adding new nodes in the middle, at the beginning or off to one side of the cable is difficult to the point where it might be easier to redeploy an entirely new cable. This procedure is very costly since the cable itself, and its deployment in the ocean are the largest single system cost.
The present invention method and apparatus of allowing parallel branches to be effectively placed in series with any other branch while still maintaining the basic power delivery requirements permit more flexibility and better cable usage by allowing wide branching to provide a treelike structure, more efficient coverage, i.e., less cable use over a given area is provided. Moreover, the cable does not have to wind back and forth to cover a certain shaped area. The cable length is minimized, thereby minimizing insulation costs. Moreover, minimizing cable length minimizes power loss as the result of the cable resistance which is proportional to the length.
The present invention also allows relatively easy modification of the original installation. Simply cutting the cable at any location along the main branch, a parallel branch may be introduced. If desired, provisions may be made at the time of installation of the main branch to add parallel branches in the future, further simplifying the future modification of the main branch while minimizing expenditures required for expansion.